The present invention relates to a straight traveling apparatus, more specifically, a straight traveling apparatus for a construction machine and a control method thereof, which allows a curved travel when the working devices (boom, arm, etc.) are operated during a travel.
FIG. 1 shows a hydraulic circuit of the straight traveling apparatus which controls the straight travel valve electrically according to the prior art.
As shown in FIG. 1, the first and second variable displacement hydraulic pumps (hereinafter, the first and second hydraulic pumps) (1, 2) and the pilot pump (17) are connected to the engine (not shown).
A first travel control valve (5) and first working control valves (6, 7) are installed in a flow path (3) that is connected to the first hydraulic pump (1). The first travel control valve (5) controls the hydraulic oil that is supplied to the left travel motor (4), and the first working device switch valves (6, 7) controls the hydraulic oil that is supplied to the first working device (e.g. arm).
A second travel control valve (10) and second working control valves (11, 12) are installed in a flow path (8) that is connected to the second hydraulic pump (2). The second travel control valve (10) controls the hydraulic oil that is supplied to the right travel motor (9), and the second working device control valves (11, 12) controls the hydraulic oil that is supplied to the second working device (e.g. boom).
The straight travel valve (14) is installed at an upstream of the flow path (8), which is switched by the pilot pressure applied from the electrical control valve. When the working device, e.g. boom, is operated during a travel, the straight travel control valve (14) is switched so that the hydraulic oil of the first hydraulic pump (1) is supplied to the left travel motor (4) and right travel motor (9), respectively, while the hydraulic oil of the second hydraulic pump (2) is supplied to the first working device and the second working device, respectively.
Thus, some of the hydraulic oil of the first hydraulic pump (1) is supplied to the left travel motor (4) by way of the flow path (3) and the first travel control valve (5), and the rest of the hydraulic oil of the first hydraulic pump (1) is supplied to the first working device by way of the flow paths (3, 15), straight travel valve (14), and first working device switch valve (6, 7).
Also, some of the hydraulic oil of the second hydraulic pump (2) is supplied to the right travel motor (4) by way of the path (8), the straight travel valve (14) and the second travel control valve (10), and the rest of the hydraulic oil of the second hydraulic pump (2) is supplied to the second working device by way of the flow paths (8, 16) and the second working device switch valves (11, 12).
On the other hand, when the working device, e.g. boom, is operated during the travel, the spool of the straight traveling control valve (14) is switched to the right direction in the drawing by the pilot pressure applied from the electrical control valve.
Due to this spool switching, some of the hydraulic oil of the first hydraulic pump (1) is supplied to the left traveling motor (4) by way of the flow path (3) and the first travel control valve (5), and the rest of the hydraulic oil of the first hydraulic pump (1) is supplied to the right travel motor (9) by way of the flow paths (3, 15), the straight travel valve (14), and the second travel control valve (10). Meanwhile, some of the hydraulic oil of the second hydraulic pump (2) is supplied to the first working device by way of the flow path (8), the straight travel valve (14) and the first working device switch valves (6, 7), and the rest of the hydraulic oil of the second hydraulic pump (2) is supplied to the second working device by way of the flow paths (8, 16) and the second working device switch valves (11, 12).
As described above, when the working device, e.g. boom, is operated during the travel, the hydraulic oil of the first hydraulic pump (1) is supplied to the left travel motor (4) and right travel motor (9), respectively, while the hydraulic oil of the second hydraulic pump (2) is supplied to the first working device and the second working device, respectively.
Hence, in case that the working device is operated during the travel, the apparatus can move straight as the single travel can be prevented due to the overload applied to the working device.
FIG. 2 shows the hydraulic circuit of the straight travel apparatus which controls the straight travel valve hydraulically.
As shown in FIG. 2, when the working device, e.g. boom, is operated during the travel, the straight travel valve (14) is switched so that the hydraulic oil of the first hydraulic pump (1) is supplied to the left travel motor (4) and right travel motor (9), respectively, while the hydraulic oil of the second hydraulic pump (2) is supplied to the first working device and the second working device, respectively. The straight travel control valve (14) is installed in the upper side of the path (8), and switched by the pilot pressure applied from the pilot pump (17).
In this case, since the configuration is same as that in FIG. 1 except the pilot pump, the detailed description will be abbreviated with same reference numerals for the overlapping parts in the drawing.
FIG. 3 shows the drive track according to the prior art when the working device is operated during a curved travel.
As shown in FIG. 3, when the working device is operated simultaneously with a straight traveling apparatus in a combined operation with a curved travel along the drive track, the straight travel valve (14) is switched to make a straight travel, and the machine is not put under the curved travel. Thus, when the straight travel valve (14) is switched during the curved travel, it may cause the safety problem to occur since the machine moves straight against the driver's intention for the curved travel.
Accordingly, it is desirable to provide a straight traveling apparatus for the construction machine and a control method thereof, which secures the safety by the curved travel at the driver's intention when the working devices are operated during the curved travel.
In accordance with an aspect of the present invention, there is provided a straight traveling apparatus for a construction machine comprising:
a first and a second variable displacement hydraulic pump and a pilot pump;
a left travel motor and a first working device that are operated by the first variable displacement hydraulic pump;
a plurality of control valves that are installed in a flow path of the first hydraulic pump and control the hydraulic oil supplied to the left travel motor or the first working device;
a right travel motor and a second working device that are operated by the second variable displacement hydraulic pump;
a plurality of control valves that are installed in a flow path of the second variable displacement hydraulic pump and control the hydraulic oil supplied to the right travel motor or the second working device;
a straight travel valve that is switched by the pilot pressure operated by an electrical control valve, the straight travel valve, when being switching, supplying the hydraulic oil of one of the first and second hydraulic variable displacement pumps to the left and right travel motors while supplying the hydraulic oil of the other of the first and second variable displacement hydraulic pumps to the left and right working devices;
a pressure detection sensor for detecting the pilot pressure applied to the left and right travel motor control valves and the pilot pressure applied to the first and second working device control valves; and
a controller that outputs a control signal to the electrical control valve so that the pilot pressure applied to the straight travel valve is blocked in case that the difference between the pilot pressures applied to the left and right travel motor control valves is larger than the pre-set pressure value, when the first and second working devices are operated during a travel.
According to the embodiment of an aspect of the present invention having the above-described configuration, a method for controlling a straight traveling apparatus for a construction machine including a left travel motor and a first working device that are operated by a first variable displacement hydraulic pump; a first working device control valve that is installed in a flow path that is connected to the first variable displacement hydraulic pimp; a right travel motor and a second working device that are operated by a second variable displacement hydraulic pump; a second working device control valve that is installed in a flow path that is connected to the second variable displacement hydraulic pump; a straight travel valve that is switched by a pilot pressure applied from an electrical control valve; a pressure detection sensor for detecting the pilot pressures applied to left and right travel motor control valves as well as the first and second working device control valves; and a controller to which the detection signal from the pressure detection sensor is inputted, the method comprising:
a step of detecting the pilot pressures applied to the left and right travel motor control valves as well as the pilot pressures applied to the first and second working device control valves;
a step of calculating a pressure difference between the pilot pressures applied to the left and right travel motor control valves;
a step of comparing the calculated pressure difference with the pre-set pressure value, when the first and second working devices are operated during a travel; and
a step of blocking the pilot pressure applied to the straight travel valve from the electrical control valve by recognizing the a curved travel mode when the calculated pressure difference is larger than the pre-set pressure value.
According to another embodiment of an aspect of the present invention having the above-described configuration, a straight traveling apparatus for a construction machine comprising:
a first and a second variable displacement hydraulic pumps and a pilot pump;
a left travel motor and a first working device that are operated by the first variable displacement hydraulic pump;
a plurality of control valves that are installed in a path that is connected to the first variable displacement hydraulic pump and control the hydraulic oil supplied to the left travel motor or the first working device;
a right travel motor and a second working device that are operated by the second variable displacement hydraulic pump;
a plurality of control valves that are installed in a path that is connected to the second variable displacement hydraulic pump and control the hydraulic oil supplied to the right travel motor or the second working device;
a straight travel valve that is switched by a pilot pressure applied from the pilot pump and supplies an hydraulic oil that is discharged from one of the first and second variable displacement hydraulic pumps to the left and right travel motors while supplying an hydraulic oil that is discharged from the other of the first and second variable displacement hydraulic pumps to the left and right working devices; and
a straight travel detection valve that is installed in a flow path between the pilot pump and the straight travel valve,
wherein the straight travel detection valve is switched and blocks the pilot pressure applied to the straight travel valve in case that a pressure difference between the pilot pressures applied to the left and right travel motor control valves is larger than the pre-set pressure value of a valve spring at both ends of the straight travel detection valve, when the first and second working devices are operated during a travel.
Preferably, the electrical control valve includes a solenoid valve, the proportional pressure reducing valve being adjusted to allow the pilot pressure from the pilot pump to the straight travel valve, in response to an electrical signal that is applied from the controller.
More preferably, the electrical control valve includes a proportional pressure reducing valve, wherein an hydraulic oil supplied from the pilot pump is converted to a pilot pressure in response to the electrical signal applied from the controller, and the pilot pressure is applied to the straight travel valve.
A first and second shuttle valves are provided, the first shuttle valve for selecting the pilot pressure which is relatively higher between the pilot pressures at both ends of the left travel motor control valve, and applying the selected pilot pressure to one pressure receiving port of the straight travel detection valve; and the second shuttle valve for selecting the pilot pressure which is relatively higher between the pilot pressures at both ends of the right travel motor control valve, and applying the selected pilot pressure to the other pressure receiving port of the straight travel detection valve.
When the difference between the pilot pressures is below the pre-set pressure value, the straight travel mode is recognized and the pilot pressure from the electrical control valve is applied to the straight travel valve to be switched.
According to an aspect of the present invention having the configuration described above, when the working device is operated simultaneously with the straight traveling apparatus in a combined operation during the curved travel, the straight travel mode is blocked and the machine is allowed for the curved travel, so that it has the effect of protecting the driver and machine from the safety accident.
                1; first variable displacement hydraulic pump        2; second hydraulic pump        3, 8; flow path        4; left travel motor        5; first travel motor control valve        6; first working device control valve        9; right travel motor        10; second travel motor control valve        11; second working device control valve        13; electrical control valve        14; straight travel valve        17, 18, 21, 22; pressure sensor        19, 20; joystick        23; controller        24; first shuttle valve        25; second shuttle valve        26; straight travel detection valve        27, 27a; drive pedal        